Method for transmitting D2D signal of terminal in D2D communication, and device for same

ABSTRACT

A method of transmitting a device-to-device (D2D) signal by a user equipment (UE) in D2D communication is disclosed. The method for transmitting a D2D signal includes the steps of performing frequency hopping for physical resource blocks (PRBs) in a resource block pool based on a predefined hopping patter, and transmitting a D2D signal using the PRBs. The resource block pool is configured by means of higher layer signaling and the transmission of the D2D signal occurs only when PRBs for transmitting the D2D signal are consecutive in a subframe.

This application is a National Stage Application of InternationalApplication No. PCT/KR2015/008321, filed on Aug. 7, 2015, which claimsthe benefit of U.S. Provisional Application No. 62/034,746, filed onAug. 7, 2014, all of which are hereby incorporated by reference in theirentirety for all purposes as if fully set forth herein.

TECHNICAL FIELD

The present invention relates to a wireless communication system,particularly, to a method for transmitting a D2D signal of a terminal inD2D (Device to Device) communication and a device for the same.

BACKGROUND ART

Recently, with the spread of smartphones and tablet PCs and activationof high-capacity multimedia communication, mobile traffic hassignificantly increased. Mobile traffic is expected to double everyyear. Since most mobile traffic is transmitted through a eNB (BS),communication service operators are being confronted with seriousnetwork load. To process increasing traffic, communication operatorshave installed networks and accelerated commercialization ofnext-generation mobile communication standards, such as mobile WiMAX orlong term evolution (LTE), capable of efficiently processing largeamounts of traffic. However, another solution is required to cope withgreater amounts of traffic in the future.

D2D communication refers to decentralized communication technology fordirectly transmitting traffic between contiguous nodes without usinginfrastructure such as a BS. In a D2D communication environment, eachnode of a portable device, etc. searches for physically adjacentdevices, configures a communication session, and transmits traffic.Since such D2D communication is being spotlighted as the technologicalbasis of next-generation mobile communication after 4G due to abilitythereof to cope with traffic overload by distributing traffic convergingupon the BS. For this reason, a standardization institute such as 3rdgeneration partnership (3GPP) or institute of electrical and electronicsengineers (IEEE) is establishing D2D communication standards based onLTE-advanced (LTE-A) or Wi-Fi and Qualcomm etc. have developedindependent D2D communication technology.

D2D communication is expected not only to contribute to increasedperformance of a mobile communication system but also to create a newcommunication service. Further, an adjacency based social networkservice or a network game service can be supported. A connectivityproblem of a device in a shadow area can be overcome using a D2D link asa relay. Thus, D2D technology is expected to provide new services invarious fields.

In fact, D2D communication, such as infrared communication, ZigBee,radio frequency identification (RFID), and near field communication(NFC) based on RFID, has already been widely used. However, strictlyspeaking, it is difficult for these technologies to be classified as D2Dcommunication for decentralizing traffic of a BS because they supportonly special communication purposes within a significantly limiteddistance (around 1 m).

In order to increase link reliability in D2D communication, frequencyhopping may be used. However, a method for performing frequency hoppingin D2D communication has not been specifically proposed.

DISCLOSURE Technical Problem

An object of the present invention devised to solve the problem lies ina method for determining a resource block by performing frequencyhopping in D2D communication.

It is another object of the present invention to provide a method forperforming frequency hopping in a non-contiguous D2D resource pool.

It will be appreciated by persons skilled in the art that the objectsthat could be achieved with the present invention are not limited towhat has been particularly described hereinabove and the above and otherobjects that the present invention could achieve will be more clearlyunderstood from the following detailed description.

Technical Solution

The object of the present invention can be achieved by providing amethod for transmitting a D2D signal of a terminal in D2D(Device-to-Device) communication, the method including transmitting aD2D signal using physical resource blocks in a resource block pool,wherein configuration of the resource block pool is indicated by higherlayer signaling, wherein the transmission of the D2D signal occurs onlyon contiguous physical resource blocks.

In another aspect of the present invention, provided herein is aterminal for transmitting a D2D signal in D2D (Device-to-Device)communication, including a radio frequency unit, and a processorconfigured to control the radio frequency unit, the processor beingfurther configured to transmit a D2D signal using physical resourceblocks in a resource block pool, wherein configuration of the resourceblock pool is indicated by higher layer signaling, wherein thetransmission of the D2D signal occurs only on contiguous physicalresource blocks.

Advantageous Effects

According to embodiments of the present invention, D2D frequency hoppingmay be performed using conventional LTE type ½ PUSCH hopping.

According to embodiments of the present invention, frequency hopping maybe performed between different frequency resources to obtain improvedfrequency diversity.

It will be appreciated by persons skilled in the art that the effectsthat may be achieved with the present invention are not limited to whathas been particularly described hereinabove and other advantages of thepresent invention will be more clearly understood from the followingdetailed description taken in conjunction with the accompanyingdrawings.

DESCRIPTION OF DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention and are incorporated in and constitute apart of this application, illustrate embodiments of the invention andtogether with the description serve to explain the principle of theinvention.

FIG. 1 is a block diagram illustrating configurations of a eNB (BS) anda user equipment (UE) in a wireless communication system.

FIG. 2 exemplarily shows a radio frame structure.

FIG. 3 exemplarily shows a resource grid of one downlink slot.

FIG. 4 exemplarily shows a downlink (DL) subframe structure.

FIG. 5 exemplarily shows an uplink (UL) subframe structure.

FIG. 6 is a diagram for a configuration of a general MIMO communicationsystem.

FIG. 7 is a diagram illustrating a structure of a downlink referencesignal for a normal CP in an LTE system supporting downlink transmissionusing four antennas.

FIG. 8 is a diagram illustrating a structure of a downlink referencesignal for an extended CP in an LTE system supporting downlinktransmission using four antennas.

FIG. 9 illustrates an example of a periodic CSI-RS transmission scheme.

FIG. 10 illustrates an example of an aperiodic CSI-RS transmissionscheme.

FIG. 11 shows a simplified D2D communication network.

FIG. 12 illustrates configuration of a resource unit according to anembodiment.

FIG. 13 illustrates a periodic SA resource pool according to anembodiment.

FIG. 14 illustrates an example of type 1 PUSCH hopping.

FIG. 15 illustrates an example of type 2 PUSCH hopping.

FIG. 16 illustrates a D2D resource pool according to an embodiment.

BEST MODE

The following embodiments are achieved by combination of structuralelements and features of the present invention in a predetermined type.Each of the structural elements or features should be consideredselectively unless specified separately. Each of the structural elementsor features may be carried out without being combined with otherstructural elements or features. Also, some structural elements and/orfeatures may be combined with one another to constitute the embodimentsof the present invention. The order of operations described in theembodiments of the present invention may be changed. Some structuralelements or features of one embodiment may be included in anotherembodiment, or may be replaced with corresponding structural elements orfeatures of another embodiment.

In this specification, the embodiments of the present invention havebeen described based on the data transmission and reception between aeNB BS and a user equipment UE. In this case, the eNB BS means aterminal node of a network, which performs direct communication with theuser equipment UE. A specific operation which has been described asbeing performed by the eNB may be performed by an upper node of the eNBBS as the case may be.

In other words, it will be apparent that various operations performedfor communication with the user equipment UE in the network whichincludes a plurality of network nodes along with the eNB may beperformed by the eNB BS or network nodes other than the eNB BS. At thistime, the eNB BS may be replaced with terms such as a fixed station,Node B, eNode B (eNB), and an access point (AP). A relay node may bereplaced with terms such as a relay node (RN) and a relay station (RS).Also, a terminal may be replaced with terms such as a user equipment(UE), a mobile station (MS), a mobile subscriber station (MSS), and asubscriber station (SS).

Specific terminologies hereinafter used in the embodiments of thepresent invention are provided to assist understanding of the presentinvention, and various modifications may be made in the specificterminologies within the range that they do not depart from technicalspirits of the present invention.

In some cases, to prevent the concept of the present invention frombeing ambiguous, structures and apparatuses of the known art will beomitted, or will be shown in the form of a block diagram based on mainfunctions of each structure and apparatus. Also, wherever possible, thesame reference numbers will be used throughout the drawings and thespecification to refer to the same or like parts.

The embodiments of the present invention may be supported by standarddocuments disclosed in at least one of wireless access systems, i.e.,IEEE 802 system, 3GPP system, 3GPP LTE system, 3GPP LTE, 3GPP LTE-A(LTE-Advanced) system, and 3GPP2 system. Namely, among the embodimentsof the present invention, apparent steps or parts, which are notdescribed to clarify technical spirits of the present invention, may besupported by the above documents. Also, all terminologies disclosedherein may be described by the above standard documents.

The following technology may be used for various wireless access systemssuch as CDMA (code division multiple access), FDMA (frequency divisionmultiple access), TDMA (time division multiple access), OFDMA(orthogonal frequency division multiple access), and SC-FDMA (singlecarrier frequency division multiple access). The CDMA may be implementedby the radio technology such as universal terrestrial radio access(UTRA) or CDMA2000. The TDMA may be implemented by the radio technologysuch as global system for mobile communications (GSM)/general packetradio service (GPRS)/enhanced data rates for GSM evolution (EDGE). TheOFDMA may be implemented by the radio technology such as IEEE 802.11(Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802.20, and evolved UTRA (E-UTRA).The UTRA is a part of a universal mobile telecommunications system(UMTS). A 3rd generation partnership project long term evolution (3GPPLTE) communication system is a part of an evolved UMTS (E-UMTS) thatuses E-UTRA, and uses OFDMA in a downlink while uses SC-FDMA in anuplink. LTE-advanced (LTE-A) is an evolved version of the 3GPP LTEsystem. WiMAX may be described by the IEEE 802.16e standard(WirelessMAN-OFDMA Reference System) and the advanced IEEE 802.16mstandard (WirelessMAN-OFDMA Advanced system). Although the followingdescription will be based on the 3GPP LTE system and the 3GPP LTE-Asystem to clarify description, it is to be understood that technicalspirits of the present invention are not limited to the 3GPP LTE and the3GPP LTE-A system.

Specific terms used for the embodiments of the present invention areprovided to help the understanding of the present invention. Thesespecific terms may be replaced with other terms within the scope andspirit of the present invention.

FIG. 1 is a block diagram illustrating configurations of a eNB 105 and auser equipment 110 in a wireless communication system.

Although one eNB 105 and one user equipment (e.g., D2D UE) 110 are shownfor simplification of a wireless communication system 100, the wirelesscommunication system 100 may include one or more eNBs and/or one or moreuser equipments.

Referring to FIG. 1, the eNB 105 may include a transmitting (Tx) dataprocessor 115, a symbol modulator 120, a transmitter 125, a transmittingand receiving antenna 130, a processor 180, a memory 185, a receiver190, a symbol demodulator 195, and a receiving (Rx) data processor 297.The user equipment 110 may include a Tx data processor 165, a symbolmodulator 170, a transmitter 175, a transmitting and receiving antenna135, a processor 155, a memory 160, a receiver 140, a symbol demodulator155, and an Rx data processor 150. Although the antennas 130 and 135 arerespectively shown in the eNB 105 and the user equipment 110, each ofthe eNB 105 and the user equipment 110 includes a plurality of antennas.Accordingly, the eNB 105 and the user equipment 110 according to thepresent invention support a multiple input multiple output (MIMO)system. Also, the eNB 105 according to the present invention may supportboth a single user-MIMO (SU-MIMO) system and a multi user-MIMO (MU-MIMO)system.

On a downlink, the Tx data processor 115 receives traffic data, formatsand codes the received traffic data, interleaves and modulates (orsymbol maps) the coded traffic data, and provides the modulated symbols(“data symbols”). The symbol modulator 120 receives and processes thedata symbols and pilot symbols and provides streams of the symbols.

The symbol modulator 120 multiplexes the data and pilot symbols andtransmits the multiplexed data and pilot symbols to the transmitter 125.At this time, the respective transmitted symbols may be a signal valueof null, the data symbols and the pilot symbols. In each symbol period,the pilot symbols may be transmitted continuously. The pilot symbols maybe frequency division multiplexing (FDM) symbols, orthogonal frequencydivision multiplexing (OFDM) symbols, time division multiplexing (TDM)symbols, or code division multiplexing (CDM) symbols.

The transmitter 125 receives the streams of the symbols and converts thereceived streams into one or more analog symbols. Also, the transmitter125 generates downlink signals suitable for transmission through a radiochannel by additionally controlling (for example, amplifying, filteringand frequency upconverting) the analog signals. Subsequently, thedownlink signals are transmitted to the user equipment through theantenna 130.

In the configuration of the user equipment 110, the antenna 135 receivesthe downlink signals from the eNB 105 and provides the received signalsto the receiver 140. The receiver 140 controls (for example, filters,amplifies and frequency downcoverts) the received signals anddigitalizes the controlled signals to acquire samples. The symboldemodulator 145 demodulates the received pilot symbols and provides thedemodulated pilot symbols to the processor 155 to perform channelestimation.

Also, the symbol demodulator 145 receives a frequency responseestimation value for the downlink from the processor 155, acquires datasymbol estimation values (estimation values of the transmitted datasymbols) by performing data demodulation for the received data symbols,and provides the data symbol estimation values to the Rx data processor150. The Rx data processor 50 demodulates (i.e., symbol de-mapping),deinterleaves, and decodes the data symbol estimation values to recoverthe transmitted traffic data.

Processing based on the symbol demodulator 145 and the Rx data processor150 is complementary to processing based on the symbol demodulator 120and the Tx data processor 115 at the eNB 105.

On an uplink, the Tx data processor 165 of the user equipment 110processes traffic data and provides data symbols. The symbol modulator170 receives the data symbols, multiplexes the received data symbolswith the pilot symbols, performs modulation for the multiplexed symbols,and provides the streams of the symbols to the transmitter 175. Thetransmitter 175 receives and processes the streams of the symbols andgenerates uplink signals. The uplink signals are transmitted to the eNB105 through the antenna 135.

The uplink signals are received in the eNB 105 from the user equipment110 through the antenna 130, and the receiver 190 processes the receiveduplink signals to acquire samples. Subsequently, the symbol demodulator195 processes the samples and provides data symbol estimation values andthe pilot symbols received for the uplink. The Rx data processor 197recovers the traffic data transmitted from the user equipment 110 byprocessing the data symbol estimation values.

The processors 155 and 180 of the user equipment 110 and the eNB 105respectively command (for example, control, adjust, manage, etc.) theoperation at the user equipment 110 and the eNB 105. The processors 155and 180 may respectively be connected with the memories 160 and 185 thatstore program codes and data. The memories 160 and 185 respectivelyconnected to the processor 180 store operating system, application, andgeneral files therein.

Each of the processors 155 and 180 may be referred to as a controller, amicrocontroller, a microprocessor, and a microcomputer. Meanwhile, theprocessors 155 and 180 may be implemented by hardware, firmware,software, or their combination. If the embodiment of the presentinvention is implemented by hardware, application specific integratedcircuits (ASICs), digital signal processors (DSPs), digital signalprocessing devices (DSPDs), programmable logic devices (PLDs), and fieldprogrammable gate arrays (FPGAs) configured to perform the embodiment ofthe present invention may be provided in the processors 155 and 180.

Meanwhile, if the embodiment according to the present invention isimplemented by firmware or software, firmware or software may beconfigured to include a module, a procedure, or a function, whichperforms functions or operations of the present invention. Firmware orsoftware configured to perform the present invention may be provided inthe processors 155 and 180, or may be stored in the memories 160 and 185and driven by the processors 155 and 180.

Layers of a radio interface protocol between the user equipment 110 orthe eNB 105 and a wireless communication system (network) may beclassified into a first layer L1, a second layer L2 and a third layer L3on the basis of three lower layers of OSI (open system interconnection)standard model widely known in communication systems. A physical layerbelongs to the first layer L1 and provides an information transferservice using a physical channel. A radio resource control (RRC) layerbelongs to the third layer and provides control radio resources betweenthe user equipment and the network. The user equipment and the eNB mayexchange RRC messages with each another through the RRC layer.

While the UE processor 155 enables the UE 110 to receive signals and mayprocess other signals and data, and the BS processor 180 enables the BS105 to transmit signals and may process other signals and data, theprocessors 155 and 180 will not be specially mentioned in the followingdescription. Although the processors 155 and 180 are not speciallymentioned in the following description, it should be noted that theprocessors 155 and 180 may process not only data transmission/receptionfunctions but also other operations such as data processing and control.

LTE/LET-A Resource Structure/Channel

Hereinafter, a DL radio frame structure will be described with referenceto FIG. 2.

In a cellular OFDM wireless packet communication system, an uplink(UL)/downlink (DL) data packet is transmitted on a subframe-by-subframebasis, and one subframe is defined as a predetermined time intervalincluding a plurality of OFDM symbols. 3GPP LTE supports a type-1 radioframe structure applicable to frequency division duplex (FDD) and atype-2 radio frame structure applicable to time division duplex (TDD).Particularly, FIG. 2(a) shows a frame structure for frequency divisionduplex (FDD) used in 3GPP LTE/LTE-A and FIG. 2(b) shows a framestructure for time division duplex (TDD) used in 3GPP LTE/LTE-A.

FIG. 2(a) illustrates the type-1 radio frame structure. A radio framehas a length of 10 ms (327200×T_(s)) and is composed of 10 equal sizedsubframes. Each subframe has a length of 1 ms and is composed of twoslots. Each slot has a length of 0.5 ms (15360×c). Here, T_(s) denotesthe sampling time, and is represented by T_(s)=1/(15kHz×2048)=3.2552×10⁻⁸ (about 33 ns). A slot includes a plurality of OFDMsymbols in the time domain and a plurality of resource blocks (RB) inthe frequency domain. In the LTE system, one resource block includes 12subcarriers×7 (6) OFDM symbols. 20 slots in one radio frame may besequentially numbered from 0 to 19. Each slot has a length of 0.5 ms.The time for transmitting one subframe is defined as a transmission timeinterval (TTI). The time resource may be classified by a radio framenumber (or a radio frame index), a subframe number (or a subframeindex), a slot number (or a slot index), and the like.

FIG. 2(b) illustrates the type-2 radio frame structure. The type-2 radioframe includes two half frames, each of which has 5 subframes, adownlink pilot time slot (DwPTS), a guard period (GP), and an uplinkpilot time slot (UpPTS). Each subframe includes two slots. The DwPTS isused for initial cell search, synchronization, or channel estimation ina UE, whereas the UpPTS is used for channel estimation in an eNB and ULtransmission synchronization in a UE. The GP is provided to eliminateinterference taking place in UL due to multipath delay of a DL signalbetween DL and UL. Regardless of the type of a radio frame, a subframeof the radio frame includes two slots.

The radio frame may be configured differently according to the duplexmode. For example, in the frequency division duplex (FDD) mode, downlinktransmission and uplink transmission are divided by frequency, and thusthe radio frame includes only one of the downlink subframe and theuplink subframe for a specific frequency band. In the TDD mode, sincethe downlink transmission and the uplink transmission are divided bytime, the radio frame includes both the downlink subframe and the uplinksubframe for a specific frequency band.

Table 1 illustrates DL-UL configurations of subframes in a radio framein the TDD mode.

TABLE 1 Downlink- to-Uplink Switch- DL-UL point Subframe numberconfiguration periodicity 0 1 2 3 4 5 6 7 8 9 0 5 ms D S U U U D S U U U1 5 ms D S U U D D S U U D 2 5 ms D S U D D D S U D D 3 10 ms  D S U U UD D D D D 4 10 ms  D S U U D D D D D D 5 10 ms  D S U D D D D D D D 6 5ms D S U U U D S U U D

In Table 1, D denotes a downlink subframe, U denotes an uplink subframe,and S denotes a special subframe. The specific subframe includes threefields of Downlink Pilot Time Slot (DwPTS), Guard Period (GP), andUplink Pilot Time Slot (UpPTS). DwPTS is a time interval reserved fordownlink transmission, and UpPTS is a time interval reserved for uplinktransmission. Table 2 illustrates configurations of the specific frame.

TABLE 2 Normal cyclic prefix in downlink Extended cyclic prefix indownlink UpPTS UpPTS Special Normal cyclic Extended Normal Extendedsubframe prefix in cyclic prefix cyclic prefix cyclic prefixconfiguration DwPTS uplink in uplink DwPTS in uplink in uplink 0  6592 ·T_(s) 2192 · T_(s) 2560 · T_(s)  7680 · T_(s) 2192 · T_(s) 2560 · T_(s)1 19760 · T_(s) 20480 · T_(s) 2 21952 · T_(s) 23040 · T_(s) 3 24144 ·T_(s) 25600 · T_(s) 4 26336 · T_(s)  7680 · T_(s) 4384 · T_(s) 5120 ·T_(s) 5  6592 · T_(s) 4384 · T_(s) 5120 · T_(s) 20480 · T_(s) 6 19760 ·T_(s) 23040 · T_(s) 7 21952 · T_(s) — — — 8 24144 · T_(s) — — —

The above-described radio frame structure is merely an example, and thenumber of subframes included in a radio frame, the number of slotsincluded in a subframe, and the number of symbols included in a slot isvariable.

FIG. 3 illustrates a resource grid for a downlink slot. A downlink slotincludes 7 OFDM symbols in the time domain and an RB includes 12subcarriers in the frequency domain, which does not limit the scope andspirit of the present invention. For example, a slot includes 7 OFDMsymbols in the case of normal CP, whereas a slot includes 6 OFDM symbolsin the case of extended CP. Each element of the resource grid isreferred to as a resource element (RE). An RB includes 12×7 REs. Thenumber of RBs in a downlink slot, NDL depends on a downlink transmissionbandwidth. An uplink slot may have the same structure as a downlinkslot.

FIG. 4 illustrates a downlink subframe structure. Up to three OFDMsymbols at the start of the first slot in a downlink subframe are usedfor a control region to which control channels are allocated and theother OFDM symbols of the downlink subframe are used for a data regionto which a PDSCH is allocated. Downlink control channels used in 3GPPLTE include a physical control format indicator channel (PCFICH), aphysical downlink control channel (PDCCH), and a physical hybridautomatic repeat request (ARQ) indicator channel (PHICH). The PCFICH islocated in the first OFDM symbol of a subframe, carrying informationabout the number of OFDM symbols used for transmission of controlchannels in the subframe. The PHICH delivers a HARQacknowledgment/negative acknowledgment (ACK/NACK) signal in response toan uplink transmission. Control information carried on the PDCCH iscalled downlink control information (DCI). The DCI includes uplinkresource allocation information, downlink resource allocationinformation or an uplink transmit (Tx) power control command for anarbitrary UE group. The PDCCH delivers information about resourceallocation and a transport format for a Downlink Shared Channel(DL-SCH), resource allocation information about an Uplink Shared Channel(UL-SCH), paging information of a Paging Channel (PCH), systeminformation on the DL-SCH, information about resource allocation for ahigher-layer control message such as a Random Access Responsetransmitted on the PDSCH, a set of transmission power control commandsfor individual UEs of a UE group, transmission power controlinformation, Voice Over Internet Protocol (VoIP) activation information,etc. A plurality of PDCCHs may be transmitted in the control region. AUE may monitor a plurality of PDCCHs. A PDCCH is formed by aggregationof one or more contiguous Control Channel Elements (CCEs). A CCE is alogical allocation unit used to provide a PDCCH at a coding rate basedon the state of a radio channel. A CCE corresponds to a plurality ofREs. The format of a PDCCH and the number of available bits for thePDCCH are determined according to the correlation between the number ofCCEs and a coding rate provided by the CCEs. An eNB determines the PDCCHformat according to DCI transmitted to a UE and adds a Cyclic RedundancyCheck (CRC) to control information. The CRC is masked by an Identifier(ID) known as a Radio Network Temporary Identifier (RNTI) according tothe owner or usage of the PDCCH. If the PDCCH is directed to a specificUE, its CRC may be masked by a cell-RNTI (C-RNTI) of the UE. If thePDCCH carries a paging message, the CRC of the PDCCH may be masked by aPaging Indicator Identifier (P-RNTI). If the PDCCH carries systeminformation, particularly, a System Information Block (SIB), its CRC maybe masked by a system information ID and a System Information RNTI(SI-RNTI). To indicate that the PDCCH carries a Random Access Responsein response to a Random Access Preamble transmitted by a UE, its CRC maybe masked by a Random Access-RNTI (RA-RNTI).

FIG. 5 illustrates an uplink subframe structure. An uplink subframe maybe divided into a control region and a data region in the frequencydomain. A physical uplink control channel (PUCCH) carrying uplinkcontrol information is allocated to the control region and a physicaluplink shared channel (PUSCH) carrying user data is allocated to thedata region. To maintain single carrier property, a UE does not transmita PUSCH and a PUCCH simultaneously. A PUCCH for a UE is allocated to anRB pair in a subframe. The RBs of the RB pair occupy differentsubcarriers in two slots. Thus it is said that the RB pair allocated tothe PUCCH is frequency-hopped over a slot boundary.

Multiple Antenna System

In the multiple antenna technology, reception of one whole message doesnot depend on a single antenna path. Instead, in the multiple antennatechnology, data fragments received through multiple antennas arecollected and combined to complete data. If the multiple antennatechnology is used, a data transfer rate within a cell region of aspecific size may be improved, or system coverage may be improved whileensuring a specific data transfer rate. In addition, this technology maybe broadly used by mobile communication devices and relays. Due to themultiple antenna technology, restriction on mobile communication trafficbased on a legacy technology using a single antenna may be solved.

FIG. 6(a) shows the configuration of a wireless communication systemincluding multiple antennas. As shown in FIG. 6(a), the number oftransmit (Tx) antennas and the number of Rx antennas respectively to NTand NR, a theoretical channel transmission capacity of the MIMOcommunication system increases in proportion to the number of antennas,differently from the above-mentioned case in which only a transmitter orreceiver uses several antennas, so that transmission rate and frequencyefficiency may be greatly increased. In this case, the transfer rateacquired by the increasing channel transmission capacity maytheoretically increase by a predetermined amount that corresponds tomultiplication of a maximum transfer rate (Ro) acquired when one antennais used and a rate of increase (Ri). The rate of increase (Ri) may berepresented by the following equation 1.R _(i)=min(N _(T) ,N _(R))  [Equation 1]

For example, provided that a MIMO system uses four Tx antennas and fourRx antennas, the MIMO system may theoretically acquire a high transferrate which is four times higher than that of a single antenna system.After the above-mentioned theoretical capacity increase of the MIMOsystem was demonstrated in the mid-1990s, many developers began toconduct intensive research into a variety of technologies which maysubstantially increase data transfer rate using the theoretical capacityincrease. Some of the above technologies have been reflected in avariety of wireless communication standards, for example,third-generation mobile communication or next-generation wireless LAN,etc.

A variety of MIMO-associated technologies have been intensivelyresearched by many companies or developers, for example, research intoinformation theory associated with MIMO communication capacity undervarious channel environments or multiple access environments, researchinto a radio frequency (RF) channel measurement and modeling of the MIMOsystem, and research into a space-time signal processing technology.

Mathematical modeling of a communication method for use in theabove-mentioned MIMO system will hereinafter be described in detail. Asmay be seen from FIG. 6(a), it is assumed that there are N_(T) Txantennas and N_(R) Rx antennas. In the case of a transmission signal, amaximum number of transmission information pieces is N_(T) under thecondition that N_(T) Tx antennas are used, so that the transmissioninformation may be represented by a specific vector shown in thefollowing equation 2.s=[s ₁ ,s ₂ , . . . ,s _(N) _(T) ]^(T)  [Equation 2]

In the meantime, individual transmission information pieces s₁, s₂, . .. , s_(NT) may have different transmission powers. In this case, if theindividual transmission powers are denoted by P₁, P₂, . . . , P_(NT),transmission information having an adjusted transmission power may berepresented by a specific vector shown in the following equation 3.ŝ=└ŝ ₁ ,ŝ ₂ , . . . ,ŝ _(N) _(T) ┘^(T)=[Ps ₁ ,Ps ₂ , . . . ,Ps _(N) _(T)]^(T)  [Equation 3]

In Equation 3, ŝ is a transmission vector, and may be represented by thefollowing equation 4 using a diagonal matrix P of a transmission power.

$\begin{matrix}{\hat{s} = {{\begin{bmatrix}P_{1} & \; & \; & 0 \\\; & P_{2} & \; & \; \\\; & \; & \ddots & \; \\0 & \; & \; & P_{N_{T}}\end{bmatrix}\begin{bmatrix}S_{1} \\S_{2} \\\vdots \\S_{N_{T}}\end{bmatrix}} = {Ps}}} & \left\lbrack {{Equation}\mspace{14mu} 4} \right\rbrack\end{matrix}$

In the meantime, the information vector ŝ having an adjustedtransmission power is applied to a weight matrix W, so that N_(T)transmission signals x₁, x₂, . . . , x_(NT) to be actually transmittedare configured. In this case, the weight matrix W is adapted to properlydistribute transmission information to individual antennas according totransmission channel situations. The above-mentioned transmissionsignals x₁, x₂, . . . , x_(NT) may be represented by the followingequation 5 using the vector X. Here, W_(ij) denotes a weightcorresponding to i-th Tx antenna and j-th information. W represents aweight matrix or precoding matrix.

$\begin{matrix}\begin{matrix}{x = \begin{bmatrix}x_{1} \\x_{2} \\\vdots \\x_{i} \\\vdots \\x_{N_{T}}\end{bmatrix}} \\{= {\begin{bmatrix}w_{11} & w_{12} & \ldots & w_{1N_{T}} \\w_{12} & w_{12} & \ldots & w_{2N_{T}} \\\vdots & \; & \ddots & \; \\w_{i\; 2} & w_{i\; 2} & \ldots & w_{{iN}_{T}} \\\vdots & \; & \ddots & \; \\w_{N_{T}1} & w_{N_{T}2} & \ldots & w_{N_{T}N_{T}}\end{bmatrix}\begin{bmatrix}{\hat{s}}_{1} \\{\hat{s}}_{2} \\\vdots \\{\hat{s}}_{j} \\\vdots \\{\hat{s}}_{N_{T}}\end{bmatrix}}} \\{= {W\hat{s}}} \\{= {WPs}}\end{matrix} & \left\lbrack {{Equation}\mspace{14mu} 5} \right\rbrack\end{matrix}$

Given N_(R) Rx antennas, signals received at the respective Rx antennas,y₁, y₂, . . . , y_(N) _(R) may be represented as the following vector.y=[y ₁ ,y ₂ , . . . ,y _(N) _(R) ]^(T)  [Equation 6]

When channels are modeled in the MIMO communication system, they may bedistinguished according to the indexes of Tx and Rx antennas and thechannel between a j^(th) Tx antenna and an i^(th) Rx antenna may berepresented as h_(ij). It is to be noted herein that the index of the Rxantenna precedes that of the Tx antenna in h_(ij).

The channels may be represented as vectors and matrices by groupingthem. Examples of vector expressions are given as below. FIG. 6(b)illustrates channels from N_(T) Tx antennas to an i^(th) Rx antenna.

As illustrated in FIG. 6(b), the channels from the N_(T) Tx antennas toan i^(th) Rx antenna may be expressed as follows.h _(i) ^(T)=[h _(i1) ,h _(i2) , . . . ,h _(iN) _(T) ]  [Equation 7]

Also, all channels from the N_(T) Tx antennas to the N_(R) Rx antennasmay be expressed as the following matrix.

$\begin{matrix}{H = {\begin{bmatrix}h_{1}^{T} \\h_{2}^{T} \\\vdots \\h_{i}^{T} \\\vdots \\h_{N_{R}}^{T}\end{bmatrix} = \begin{bmatrix}h_{11} & h_{12} & \ldots & h_{1N_{T}} \\h_{12} & h_{12} & \ldots & h_{2N_{T}} \\\vdots & \; & \ddots & \; \\h_{i\; 2} & h_{i\; 2} & \ldots & h_{{iN}_{T}} \\\vdots & \; & \ddots & \; \\h_{N_{R}1} & h_{N_{R}2} & \ldots & h_{N_{R}N_{T}}\end{bmatrix}}} & \left\lbrack {{Equation}\mspace{14mu} 8} \right\rbrack\end{matrix}$

Actual channels experience the above channel matrix H and then are addedwith Additive White Gaussian Noise (AWGN). The AWGN n₁, n₂, . . . ,n_(N) _(R) added to the N_(R) Rx antennas is given as the followingvector.n=[n ₁ ,n ₂ , . . . ,n _(N) _(R) ]^(T)  [Equation 9]

From the above modeled equations, the received signal may be expressedas follows.

$\begin{matrix}\begin{matrix}{y = \begin{bmatrix}y_{1} \\y_{2} \\\vdots \\y_{i} \\\vdots \\y_{N_{R}}\end{bmatrix}} \\{= {{\begin{bmatrix}h_{11} & h_{12} & \ldots & h_{1N_{T}} \\h_{12} & h_{12} & \ldots & h_{2N_{T}} \\\vdots & \; & \ddots & \; \\h_{i\; 2} & h_{i\; 2} & \ldots & h_{{iN}_{T}} \\\vdots & \; & \ddots & \; \\h_{N_{R}1} & h_{N_{R}2} & \ldots & h_{N_{R}N_{T}}\end{bmatrix}\begin{bmatrix}x_{1} \\x_{2} \\\vdots \\x_{j} \\\vdots \\x_{N_{T}}\end{bmatrix}} + \begin{bmatrix}n_{1} \\n_{2} \\\vdots \\n_{i} \\\vdots \\n_{N_{R}}\end{bmatrix}}} \\{= {{Hx} + n}}\end{matrix} & \left\lbrack {{Equation}\mspace{14mu} 10} \right\rbrack\end{matrix}$

In the meantime, the numbers of rows and columns in the channel matrix Hrepresenting channel states are determined according to the numbers ofTx and Rx antennas. The number of rows is identical to that of Rxantennas, N_(R) and the number of columns is identical to that of Txantennas, N_(T). Thus, the channel matrix H is of size N_(R)×N_(T). Ingeneral, the rank of a matrix is defined as the smaller between thenumbers of independent rows and columns. Accordingly, the rank of thematrix is not larger than the number of rows or columns. The rank of thematrix H, rank(H) is limited as follows.rank(H)≤min(N _(T) ,N _(R))  [Equation 11]

As a multi-antenna transmission and reception scheme used for operatinga multi-antenna system, it may be able to use FSTD (frequency switchedtransmit diversity), SFBC (Space Frequency Block Code), STBC (Space TimeBlock Code), CDD (Cyclic Delay Diversity), TSTD (time switched transmitdiversity) and the like. In a rank 2 or higher, SM (SpatialMultiplexing), GCDD (Generalized Cyclic Delay Diversity), S-VAP(Selective Virtual Antenna Permutation) and the like may be used.

The FSTD corresponds to a scheme of obtaining a diversity gain byassigning a subcarrier of a different frequency to a signal transmittedby each of multiple antennas. The SFBC corresponds to a scheme capableof securing both a diversity gain in a corresponding dimension and amulti-user scheduling gain by efficiently applying selectivity in aspatial domain and a frequency domain. The STBC corresponds to a schemeof applying selectivity in a spatial domain and a time domain. The CDDcorresponds to a scheme of obtaining a diversity gain using path delaybetween transmission antennas. The TSTD corresponds to a scheme ofdistinguishing signals transmitted by multiple antennas from each otheron the basis of time. The spatial multiplexing (SM) corresponds to ascheme of increasing a transfer rate by transmitting a different dataaccording to an antenna. The GCDD corresponds to a scheme of applyingselectivity in a time domain and a frequency domain. The S-VAPcorresponds to a scheme of using a single precoding matrix. The S-VAPmay be classified into an MCW (multi codeword) S-VAP for mixing multiplecodewords between antennas in spatial diversity or spatial multiplexingand an SCW (single codeword) S-VAP for using a single codeword.

Reference Signal Received Power (RSRP)

RSRP is defined as the linear average of powers of resource elementsthat carry a cell-specific RS (CRS) within a measured frequencybandwidth. The UE may determine RSRP by detecting a cell-specificreference signal (CRS) mapped onto a specific resource element andtransmitted. The RSRP calculation may basically use CRS R0 for antennaport 0. If the terminal is capable of reliably detecting CRS R1 forantenna port 1, the UE may determine RSRP using R1 as well as R0. Fordetails of the CRS, a standard document (e.g., 3GPP TS36.211) may bereferenced.

Received Signal Strength Indicator (RSSI)

RSSI may be defined as the total received wideband power from allsources including co-channel serving and non-serving cells, adjacentchannel interference and thermal noise in a measurement band observed bythe UE. The RSSI may be used as an input to a reference signal receptionquality (RSRQ) to be described later.

Reference Signal Received Quality (RSRQ)

RSRQ, which is intended to provide cell-specific signal qualitycharacteristics, is similar to RSRP, but may be mainly used to rankdifferent LTE candidate cells according to the signal quality of eachcell. For example, if the RSRP measurement provides information that isnot sufficient to perform a reliable mobility determination, the RSRQmeasurement may be used as an input for handover and cell reselectiondecisions. RSRQ is a value obtained by dividing a value obtained bymultiplying the number N of resource blocks in the frequency bandwidthby the LTE carrier RSSI (i.e., RSRQ=N×RSRP/(E-UTRA carrier RSSI)). Thenumerator (N×RSRP) and denominator (E-UTRA carrier RSSI) are measuredfor the same set of resource blocks. While RSRP is an indicator of thedesired signal strength, RSRQ may be able to report the combined effectof signal strength and interference in an effective way by consideringthe level of interference included in the RSSI.

Reference Signal (RS)

In a mobile communication system, a packet is transmitted through awireless channel, and thus signal distortion may occur. In order tocorrect a distorted signal on the receiving side, the receiving sideneeds to know the channel information. Therefore, in order to find thechannel information, the transmitting side transmits a signal known toboth the transmitting side and the receiving side and the receiving sidefinds the information of the channel based on the degree of distortionof the received signal. In this case, a signal known to both thetransmitting side and the receiving side is referred to as a pilotsignal or a reference signal (RS). Also, in a wireless communication inwhich a multi-antenna (MIMO) technique is applied, a separate referencesignal exists for each transmission antenna.

In a mobile communication system, reference signals may be classifiedinto a reference signal for obtaining channel information and areference signal for data demodulation. Since the reference signal forobtaining channel information is intended for a UE to acquire channelinformation on the downlink, it is transmitted in a wideband. The UEthat does not receive downlink data in a specific subframe should alsobe allowed to receive and measure this RS. Also, the reference signalfor acquisition of channel information may be used for channel statemeasurement for handover. The reference signal for data demodulation isa reference signal sent together with downlink data on a downlinkresource when an eNB sends the downlink data, and the terminal mayperform channel estimation and demodulate the data by receiving thisreference signal. The reference signal for demodulation is transmittedin the region where data is transmitted.

In the LTE system, two kinds of downlink reference signals are definedfor a unicast service: a common RS (CRS) for acquisition of informationon the channel condition and measurement of, for example, handover, anda UE-specific reference signal used for data demodulation. In the LTEsystem, the UE-specific RS is used only for data demodulation and theCRS may be used for both acquisition of channel information and datademodulation. The CRS is a cell-specific signal, and may be transmittedevery subframe in the case of a wideband.

In LTE-A (LTE-Advanced), a reference signal capable of supporting amaximum of 8 transmit antennas is required. In order to support 8transmit antennas while maintaining backward compatibility with the LTEsystem, another reference signal for 8 transmit antennas needs to beadditionally defined in the time-frequency region in which a CRS definedin LTE is transmitted in every subframe in all bands. However, when areference signal for up to 8 antennas is added to the LTE-A system inthe same manner as the CRS of legacy LTE, overhead is excessivelyincreased due to the reference signal. Therefore, in LTE-A, a channelstate information-RS (CSI-RS) used for channel measurement for selectinga Modulation and Coding Scheme (MCS) and a Precision Matrix Indicatorand a DM-RS for data demodulation have been introduced. Unlike thelegacy CRS, which is used for demodulation of data as well asmeasurements such as channel measurements and handover, the CSI-RS istransmitted only for the purpose of obtaining information on channelstates. Therefore, the CSI-RS may not be transmitted every subframe. Inorder to reduce overhead caused by the CSI-RS, the CSI-RS is transmittedintermittently in the time domain, and the DM-RS for the correspondingUE is transmitted for data demodulation. Therefore, the DM-RS of aspecific terminal is transmitted only in the scheduled region, i.e., inthe time-frequency region in which the specific UE receives the data.

FIGS. 7 and 8 are diagrams showing a structure of a reference signal inthe LTE system supporting downlink transmission using four antennas.Particularly, FIG. 7 illustrates a case of a normal cyclic prefix, andFIG. 8 illustrates a case of an extended cyclic prefix.

Referring to FIGS. 7 and 8, numerals 0 to 3 in the grid indicate CommonReference Signals (CRSs), which are cell-specific reference signalstransmitted for channel measurement and data demodulation correspondingto each of antenna ports 0 to 3, The CRS, which is a cell specificreference signal, may be transmitted to the UE over the controlinformation region as well as the data information region.

In addition, ‘D’ in the grid denotes a downlink demodulation-RS (DM-RS),which is a UE-specific RS, and the DM-RS supports single antenna porttransmission through a data region, i.e., PDSCH. The UE receives asignal indicating whether there is a DM-RS, which is a UE-specific RS,through an higher layer. FIGS. 7 and 8 illustrate a DM-RS correspondingto antenna port 5, and the 3GPP standard document 36.211 also defines aDM-RS for antenna ports 7 to 14, i.e. 8 antenna ports.

For example, a rule for mapping of a reference signal to a resourceblock may be given by the following equation.

In the case of CRS, the reference signal may be mapped according toEquation 12 below.

$\begin{matrix}{k = {{6m} + \left( {{v + {v_{{shift})}{mod}\; 6l}} = \left\{ {{{\begin{matrix}{0,N_{symb}^{DL}} & {{{if}\mspace{14mu} p} \in \left\{ {0,1} \right\}} \\1 & {{{if}\mspace{14mu} p} \in \left\{ {2,3} \right\}}\end{matrix}m} = 0},1,\ldots\mspace{14mu},{{{2 \cdot N_{RB}^{DL}} - {1m^{\prime}}} = {{m + N_{RB}^{\max,{DL}} - {N_{RB}^{DL}v}} = \left\{ {{\begin{matrix}0 & {{{if}\mspace{14mu} p} = {{0\mspace{14mu}{and}\mspace{14mu} l} = 0}} \\3 & {{{if}\mspace{14mu} p} = {{0\mspace{14mu}{and}\mspace{14mu} l} \neq 0}} \\3 & {{{if}\mspace{14mu} p} = {{1\mspace{14mu}{and}\mspace{14mu} l} = 0}} \\0 & {{{if}\mspace{14mu} p} = {{1\mspace{14mu}{and}\mspace{14mu} l} \neq 0}} \\{3\left( {n_{s}{mod}\; 2} \right)} & {{{if}\mspace{14mu} p} = 2} \\{3 + {3\left( {n_{s}{mod}\; 2} \right)}} & {{{if}\mspace{14mu} p} = 3}\end{matrix}v_{shift}} = {N_{ID}^{cell}{mod}\; 6}} \right.}}} \right.} \right.}} & {{Equation}\mspace{14mu} 12}\end{matrix}$

In addition, the dedicated RS (DRS) may be mapped according to Equation13.

$\begin{matrix}{{{normal}\mspace{14mu}{CP}}{k = {\left( k^{\prime} \right){mod}\; N_{SC}^{{RB} +}{N_{SC}^{RB} \cdot n_{PRB}}}}{k^{\prime} = \left\{ {{\begin{matrix}{{4m^{\prime}} + v_{shift}} & {{{if}\mspace{14mu} l} \in \left\{ {2,3} \right\}} \\{{4m^{\prime}} + {\left( {2 + v_{shift}} \right){mod}\; 4}} & {{{if}\mspace{14mu} l} \in \left\{ {5,6} \right\}}\end{matrix}l} = \left\{ {{\begin{matrix}3 & {l^{\prime} = 0} \\6 & {l^{\prime} = 1} \\2 & {l^{\prime} = 2} \\5 & {l^{\prime} = 3}\end{matrix}l^{\prime}} = \left\{ {{{\begin{matrix}{0,1} & {{{if}\mspace{14mu} n_{s}{mod}\; 2} = 0} \\{2,3} & {{{if}\mspace{14mu} n_{s}{mod}\; 2} = 1}\end{matrix}m^{\prime}} = 0},1,\ldots\mspace{14mu},{{{3N_{RB}^{PDSCH}} - {1{Extended}\mspace{14mu}{CP}k}} = {{{\left( k^{\prime} \right){mod}\; N_{SC}^{{RB} +}{N_{SC}^{RB} \cdot n_{PRB}}}k^{\prime}} = \left\{ {{\begin{matrix}{{3m^{\prime}} + v_{shift}} & {{{if}\mspace{14mu} l} = 4} \\{{3m^{\prime}} + {\left( {2 + v_{shift}} \right){mod}\; 3}} & {{{if}\mspace{14mu} l} = 1}\end{matrix}l} = \left\{ {{\begin{matrix}4 & {l^{\prime} \in \left\{ {0,2} \right\}} \\1 & {l^{\prime} = 1}\end{matrix}l^{\prime}} = \left\{ {{{\begin{matrix}0 & {{{if}\mspace{14mu} n_{s}{mod}\; 2} = 0} \\{1,2} & {{{if}\mspace{14mu} n_{s}{mod}\; 2} = 1}\end{matrix}m^{\prime}} = 0},1,\ldots\mspace{14mu},{{{4N_{RB}^{PDSCH}} - {1v_{shift}}} = {N_{ID}^{cell}{mod}\; 3}}} \right.} \right.} \right.}}} \right.} \right.} \right.}} & {{Equation}\mspace{14mu} 13}\end{matrix}$

In Equations 12 and 13, k denotes a subcarrier index and p denotes anantenna port. In addition, N_(DL) ^(RB) denotes the number of resourceblocks allocated to downlink, n_(s) denotes a slot index, and N_(ID)^(cell) denotes a cell ID.

In the LTE-A system, the eNB transmits a CSI-RS for all antenna ports.As described above, the CSI-RS may be transmitted intermittently in thetime domain. For example, the CSI-RS may be periodically transmittedwith a period of an integer multiple of one subframe, or may betransmitted in a specific transmission pattern. In this case, theperiod/pattern in which the CSI-RS is transmitted may be set by the eNB.In order to measure a channel using the CSI-RS, the UE needs to identifya CSI-RS transmission subframe index for the CSI-RS antenna port of acell to which the UE belongs, time-frequency positions of CSI-RSelements in the transmission subframe, a CSI-RS sequence, and the like.

In the LTE-A system, the resources used for CSI-RS transmission ofdifferent antenna ports are orthogonal to each other. When an eNBtransmits CSI-RSs for different antenna ports, the CSI-RSs for therespective antenna ports may be mapped to different resource elements,such that the resource elements are allocated so as to be orthogonal toeach other in a manner of FDM/TDM. In addition, the eNB may transmit theCSI-RSs by code division multiplexing by mapping CSI-RSs for differentantenna ports using orthogonal codes.

FIG. 9 illustrates an example of a periodic CSI-RS transmission scheme.In FIG. 9, the CSI-RS is transmitted at a period of 10 ms, and theoffset is 3. A different offset value may be provided for each eNB suchthat the CSI-RSs of multiple cells may be evenly distributed. When theCSI-RS is transmitted at a period of 10 ms, the eNB may have 10 offsetvalues from 0 to 9. The offset represents an index value of a subframein which an eNB having a specific period starts CSI-RS transmission.When the eNB informs the UE of the CSI-RS period and offset value, theUE measures the CSI-RS of the eNB at the corresponding position usingthe corresponding value, and reports information such as CQI/PMI/RI tothe eNB. The information associated with the CSI-RS is all cell-specificinformation.

FIG. 10 illustrates an example of an aperiodic CSI-RS transmissionscheme. In FIG. 10, the eNB transmits a CSI-RS in subframe indexes 3 and4. The transmission pattern is composed of 10 subframes. Whether theCSI-RS is transmitted in each subframe may be designated by a bitindicator.

Generally, two methods are considered as a method for the eNB to informthe UE of the CSI-RS configuration.

First, the eNB may transmit a CSI-RS configuration using a DynamicBroadcast CHannel (DBCH) signaling for broadcasting the CSI-RSconfiguration information to UEs. In the LTE system, a BroadcastingChannel (BCH) is used to inform the UE of the content of the systeminformation. However, if not all the information can be transmitted overthe BCH because the amount of the information is large, the informationis transmitted in the same manner as typical data, and the PDCCH of thedata is CRC-masked with SI-RNTI (System Information RNTI) rather thanwith a specific UE ID. In this case, the actual system information istransmitted in the PDSCH area like general unicast data. All the UEs inthe cell may decode the PDCCH using the SI-RNTI and then decode a PDSCHindicated by the PDCCH to acquire the system information. Thebroadcasting scheme of this type is distinguished from the typicalbroadcasting scheme corresponding to the physical BCH (PBCH) and isreferred to as a DBCH. System information broadcast in the LTE system isa Master Information Block (MIB) transmitted on the PBCH and a SystemInformation Block (SIB) multiplexed with typical unicast data andtransmitted on the PDSCH. Newly introduced SIB9 in LTE-A. The CSI-RSconfiguration may be transmitted using SIB 9 or SIB 10, which is newlyintroduced in LTE-A.

In addition, the eNB may transmit CSI-RS related information to the UEusing Radio Resource Control (RRC) signaling. In establishing aconnection with an eNB through initial access or handover over, the eNBmay transmit the CSI-RS configuration to the UE using RRC signaling.Also, the eNB may transmit CSI-RS configuration information to the UEthrough an RRC signaling message for requesting feedback based on theCSI-RS measurement.

Hereinafter, various embodiments in which a UE performs device to devicecommunication (hereinafter, referred to as D2D communication or D2Ddirect communication) will be described. In describing D2Dcommunication, 3GPP LTE/LTE-A will be described as an example, but D2Dcommunication may be also applied to other communication systems (IEEE802.16, WiMAX, etc.).

D2D Communication Type

D2D communication may be classified into network coordinated D2Dcommunication and autonomous D2D communication depending on whether D2Dcommunication is performed through control of the network. Networkcoordinated D2D communication may be classified into a type (data onlyin D2D) in which D2D transmits data only and a type in which the networkperforms connection control only (connection control only in network)according to the degree of intervention of the network. For simplicity,a type in which D2D transmits data only is referred to as a‘network-concentrated D2D communication’ and a type in which the networkperforms connection control only is referred to as ‘distributed D2Dcommunication’.

In the network-concentrated D2D communication, only data is exchangedbetween D2D UEs, and connection control and radio resource allocation(grand message) between D2D UEs are performed by the network. The D2DUEs may use radio resources allocated by the network to transmit/receivedata or specific control information. For example, HARQ ACK/NACKfeedback or channel state information (CSI) for data reception betweenD2D UEs may not be directly exchanged between D2D UEs, but may betransmitted to other D2D UEs over a network. Specifically, when thenetwork establishes a D2D link between D2D UEs and allocates radioresources to the established D2D link, a transmitting D2D UE and areceiving D2D UE may perform D2D communication using the allocated radioresources. That is, in the network-concentrated D2D communication, theD2D communication between the D2D UEs is controlled by the network, andthe D2D UEs may perform D2D communication using the radio resourcesallocated by the network.

The network in the distributed D2D communication plays a more limitedrole than the network in the network-concentrated D2D communication. Inthe distributed D2D communication, the network performs connectioncontrol between D2D UEs, but radio resource allocation (grant message)between D2D UEs may be occupied by the D2D UEs through contentionwithout the help of the network. For example, HARQ ACK/NACK feedback fordata reception between D2D UEs or channel state information may bedirectly exchanged between D2D UEs without passing through the network.

As in the above example, the D2D communication may be classified intothe network-concentrated D2D communication type and the distributed D2Dcommunication type according to the degree of intervention of thenetwork in D2D communication. A common feature of thenetwork-concentrated D2D communication type and the distributed D2Dcommunication type is that D2D connection control may be performed bythe network.

Specifically, the network in the network cooperative D2D communicationmay establish a connection between D2D UEs by establishing a D2D linkbetween the D2D UEs to perform D2D communication. In establishing theD2D link between the D2D UEs, the network may assign a physical D2D linkidentifier (LID) to the established D2D link. The physical D2D link IDmay be used as an identifier for identifying each D2D link when aplurality of D2D links exist between the multiple D2D UEs.

In the autonomous D2D communication, the D2D UEs may freely perform theD2D communication without the help of the network unlike thenetwork-concentrated and distributed D2D communication types. That is,unlike the network-concentrated and distributed D2D communication, inthe autonomous D2D communication, the D2D UE autonomously performsaccess control and occupation of radio resources. If necessary, thenetwork may provide D2D channel information to the D2D UEs for use in acorresponding cell.

Configuration of D2D Communication Link

For simplicity, a UE that performs or is capable of performing D2Dcommunication, which is direct communication between UEs, will bereferred to as a D2D UE in the following description. Further, in thefollowing description, “UE” may refer to a D2D UE. When it is necessaryto distinguish between the transmitting end and the receiving end, a D2DUE that transmits or desires to transmit data to another D2D UE using aradio resource assigned to a D2D link in the D2D communication will bereferred to as a transmitting D2D UE, and a UE that receives or desiresto receive data from the transmitting D2D UE will be referred to as areceiving D2D UE. When there are a plurality of receiving D2D UEs toreceive or desire to receive data from the transmitting D2D UE, theplurality of receiving D2D UEs may be distinguished through prefixes“first” to “N-th’. Furthermore, for simplicity, any node at a networkend such as an eNB for control connection between D2D UEs or allocationof radio resources to a D2D link, a D2D server, and a connection/sessionmanagement server will be referred to as a “network.”

A D2D UE performing D2D communication needs to pre-confirm existence ofD2D UEs which are positioned nearby and capable of transmitting andreceiving data in order to transmit data to other D2D UEs through D2Dcommunication. To this end, D2D peer discovery is performed. The D2D UEperforms D2D search within a discovery interval, and all D2D UEs mayshare the discovery interval. The D2D UE may monitor the logicalchannels of a search region within the discovery interval and receiveD2D discovery signals transmitted by other D2D UEs. D2D UEs receivingthe transmitted signals of other D2D UEs generates a list of adjacentD2D UEs by using the received signals. In addition, the D2D UEs maybroadcast their information (i.e., an identifier) within the searchinverval and other D2D UE may receive the broadcast D2D discoverysignal, thereby recognizing that the corresponding D2D UE is within arange where the D2D UE is capable of performing D2D communication.

Information for D2D search may be broadcast periodically. In addition,such broadcast timing may be predetermined by a protocol and signaled tothe D2D UEs. In addition, the D2D UE may transmit/broadcast signalsduring a portion of the discovery interval, and each D2D UE may monitorsignals that are potentially transmitted by other D2D UEs in theremaining part of the D2D discovery interval.

For example, the D2D discovery signal may be a beacon signal. Also, theD2D discovery intervals may include a plurality of symbols (e.g., OFDMsymbols). The D2D UE may select at least one symbol in the D2D discoveryinterval and transmit/broadcast a D2D discovery signal. The D2D UE mayalso transmit a signal corresponding to one tone in a symbol selected bythe D2D UE.

After the D2D UEs discover each other through the D2D discoveryprocedure, the D2D UEs may perform a connection establishment procedure.For example, in FIG. 1, a first device 102 and a second device 106 maybe linked to each other through the connection procedure. Thereafter,the first device 102 may transmit traffic to the second device 106 usingthe D2D link 108. The second device 106 may also transmit traffic to thefirst device 102 using the D2D link 108.

FIG. 11 shows a simplified D2D communication network.

In FIG. 11, D2D communication is performed between UEs (UE1 and UE2)supporting D2D communication. Generally, a user equipment (UE) refers toa UE of a user. However, if a network equipment such as an evolved NodeB (eNB) transmits/receives signals according to a communication schemefor UEs (UE 1 and UE 2), it may also be regarded as an eNB or a UE.

UE1 may operate to select a resource unit corresponding to a specificresource in a resource pool, which means a set of resources, and totransmit a D2D signal using the resource unit. UE2, which serves as areceiving UE may receive configuration of a resource pool in which UE1may transmit signals and detect a signal of UE1 in the correspondingpool. For example, if UE1 is within the connection coverage of the eNB,the eNB may signal the resource pool. Further, for example, when UE1 isoutside the connection coverage of the eNB, another UE may notify UE1 ofthe resource pool or UE1 may determine the resource pool based onpredetermined resources. Generally, a resource pool includes a pluralityof resource units, and each UE may select one or more resource units anduse the same for transmission of its own D2D signal.

FIG. 12 illustrates configuration of a resource unit according to anembodiment.

In FIG. 12, the vertical axis represents frequency resources, and thehorizontal axis represents time resources. Also, a radio resource isdivided into N_(T) parts in the time domain to construct N_(T)subframes. In addition, since the frequency resource is divided intoN_(F) parts in one subframe, one subframe may include N_(T) symbols.Thus, a total of N_(F)*N_(T) resource units may be configured as aresource pool.

The D2D transmission resource (Unit #0) allocated to unit number 0 isrepeated every N_(T) subframes. Thus, in the embodiment of FIG. 12, theresource pool may be repeated with a cycle of N_(T) subframes. As shownin FIG. 12, the specific resource unit may be repeated periodically. Inaddition, in order to obtain a diversity effect in the time dimension orfrequency dimension, an index of a physical resource unit to which onelogical resource unit is mapped may be changed according to apredetermined pattern. For example, the logical resource unit may behopped in the time domain and/or frequency domain according to apredetermined pattern in an actual physical resource unit. In FIG. 12,the resource pool may mean a set of resource units that a UE desiring totransmit a D2D signal may use to transmit a signal.

The resource pools described above may be subdivided into differenttypes. For example, resource pools may be divided according to thecontent of the D2D signal transmitted in each resource pool. Forexample, the content of a D2D signal may be classified as describedbelow, and a separate resource pool may be configured for each item ofcontent.

-   -   Scheduling Assignment (SA): SA (or SA information) may include        the location of a resource used by each transmitting UE for        transmission of a subsequent D2D data channel, and a modulation        and coding scheme necessary for demodulation of the other data        channels, and/or a Multiple Input Multiple Output (MIMO)        transmission scheme. In addition, the SA information may include        a User Equipment Identifier of a target UE to which each        transmitting UE intends to transmit data. A signal containing        the SA information may be multiplexed with the D2D data on the        same resource unit and transmitted. In this case, the SA        resource pool may refer to a pool of resources in which the SA        is multiplexed and transmitted with the D2D data.    -   D2D Data Channel: The D2D data channel may refer to a pool of        resources used by a transmitting UE to transmit user data using        a resource designated through scheduling assignment. If the        scheduling assignment is allowed to be multiplexed and        transmitted together with the D2D resource data on the same        resource unit, only the D2D data channel of the form excluding        the scheduling assignment information may be transmitted in the        resource pool for the D2D data channel. That is, on the        individual resource units in the SA resource pool, a resource        element for transmitting the SA information may be used for        transmission of the D2D data on the resource pool of the D2D        data channel.    -   Discovery Message: The discovery message resource pool may refer        to a resource pool for transmitting a discovery message that        allows the transmitting UE to transmit information such as its        own ID (Identifier) to enable neighboring UEs to discover the        transmitting UE.

As described above, the D2D resource pools may be classified accordingto the content of the D2D signal. However, even if the contents of theD2D signals are the same, a different resource pool may be useddepending on the transmission/reception property of the D2D signal. Forexample, even if the same D2D data channel or discovery message is used,different resource pools may be distinguished according to atransmission timing determination method for the D2D signal (e.g.,whether the D2D signal is transmitted at a reception time of asynchronization reference signal, or transmitted at the reception timingby applying a certain timing advance), a resource allocation scheme (forexample, whether the eNB assigns the transmission resource of anindividual signal to an individual transmitting UE or whether thetransmitting UE itself selects a transmission resource of an individualsignal in a resource pool), or a signal format (e.g., the number ofsymbols occupied by each D2D signal in one subframe or the number ofsubframes used for transmission of one D2D signal).

As described above, a UE that desires to transmit data using D2Dcommunication may first select an appropriate resource from the SAresource pool and transmit its scheduling assignment (SA) information.For example, as a criterion of selection of an SA resource pool, an SAresource associated with a resource which is not used for transmissionof SA information and/or a resource which is expected not to have datatransmission in a subframe following transmission of SA information ofanother UE may be selected as an SA resource pool. The UE may alsoselect an SA resource associated with a data resource that is expectedto have a low interference level. In addition, the SA information may bebroadcast. Therefore, the UEs in the D2D communication system mayreceive the broadcast SA information. In the following description, theterm “transmission” or “transmitting” may be replaced by “broadcast”.

FIG. 13 illustrates a periodic SA resource pool according to anembodiment.

For example, an SA resource pool may precede a series of D2D datachannel resource pools. The UE first attempts to detect the SAinformation, and when existence of data that the UE needs to receive isdiscovered, the UE may attempt to receive the data on a data resourceassociated therewith. For example, the resource pool may include apreceding SA resource pool and a following data channel resource pool,as shown in FIG. 13. As shown in FIG. 13, the SA resource pool mayappear periodically. In the following description, the period in whichthe SA resource pool appears may be referred to as an SA period.

PUSCH Frequency Hopping

Hereinafter, physical uplink shared channel (PUSCH) frequency hoppingused on uplink of the current LTE communication system will bedescribed.

PUSCH hopping used in the LTE/LTE-A system may be classified into Type 1PUSCH hopping and Type 2 PUSCH hopping. Type 1 PUSCH hopping may bedetermined to be one of ¼, −¼ or ½ hopping of the hopping bandwidthaccording to a hopping bit indicated by the uplink grant DownlinkControl Information (DCI). More specifically, a physical resource block(PRB) having the lowest index in the first slot of the subframe i forPUSCH resource allocation (RA) is n_(PRB) ^(S1)(i)=RB_(START), and maybe acquired from the uplink grant. Once the lowest PRB index of thefirst slot is determined, the position of n_(PRB)(i), which is thelowest PRB index in the second slot of subframe I, may be determinedaccording to Equation 14 and Table 3 below.

$\begin{matrix}\left\{ \begin{matrix}{{n_{PRB}^{S\; 1}(i)} = {{{\overset{\sim}{n}}_{PRB}^{S\; 1}(i)} + {{\overset{\sim}{N}}_{RB}^{HO}/2}}} \\{{n_{PRB}(i)} = {{{\overset{\sim}{n}}_{PRB}(i)} + {{\overset{\sim}{N}}_{RB}^{HO}/2}}}\end{matrix} \right. & {{Equation}\mspace{14mu} 14}\end{matrix}$

TABLE 3 Number Infor- of mation System Hop- in BW ping hopping N_(RB)^(UL) bits bits ñ_(PRB)(i) 6-49 1 0 (└N_(RB) ^(PUSCH)/2┘ + ñ_(PRB)^(S1)(i))modN_(RB) ^(PUSCH) 1 Type 2 PUSCH Hopping 50-110 2 00 (└N_(RB)^(PUSCH)/4┘ + ñ_(PRB) ^(S1)(i))modN_(RB) ^(PUSCH) 01 (−└N_(RB)^(PUSCH)/4┘ + ñ_(PRB) ^(S1)(i))modN_(RB) ^(PUSCH) 10 (└N_(RB)^(PUSCH)/2┘ + ñ_(PRB) ^(S1)(i))modN_(RB) ^(PUSCH) 11 Type 2 PUSCHHopping

In Equation 14, N_(RB) ^(HO), which denotes a PUSCH-hopping offset, isprovided from an higher layer. If N_(RB) ^(HO) is an odd number, Ñ_(RB)^(HO)=N_(RB) ^(HO)+1. If N_(RB) ^(HO) is an even number, Ñ_(RB)^(HO)=N_(RB) ^(HO). In Table 3, N_(RB) ^(PUSCH), which denotes thenumber of PUSCH resource blocks, may indicate the bandwidth of frequencyhopping.

The hopping mode provided from the higher layer may determine whetherthe PUSCH frequency hopping is “inter-subframe” hopping or “intra andinter-subframe” hopping. When the hopping mode is the inter-subframemode, if the value of CURRENT_TX_NB is an even number, the PUSCHresource allocation conforms to resource allocation of the first slot.If the value of CURRENT_TX_NB is an odd number, the PUSCH resourceallocation may conform to resource allocation of the second slot.CURRENT_TX_NB indicates the number of transmissions of a transport blockthrough higher layer signaling.

FIG. 14 illustrates an example of type 1 PUSCH hopping.

In FIG. 14, the hopping bit has a value of 01. Accordingly, ñ_(PRB)(i)is (−└N_(RB) ^(PUSCH)/4┘+ñ_(PRB) ^(S1)(i))mod N_(RB) ^(PUSCH). Referringto Equation 14, n_(PRB)(i), which is a PRB number of the second slothopped by the −¼ hopping bandwidth (N_(RB) ^(PUSCH)) from the lowest PRBnumber of the first slot, may be calculated.

Type 2 PUSCH hopping, which is sub-band based hopping, may be determinedby Equation 15 below, a PRB number in slot n_(s) may be calculated inEquation 15.

$\begin{matrix}{{{{\overset{\sim}{n}}_{PRB}\left( n_{s} \right)}\left( {{\overset{\sim}{n}}_{VRB} + {{f_{hop}(i)} \cdot N_{RB}^{sb}} + {{\left( {\left( {N_{RB}^{sb} - 1} \right) - {2\left( {{\overset{\sim}{n}}_{VRB}{mod}\; N_{RB}^{sb}} \right)}} \right) \cdot {f_{m}(i)}}{mod}\;{N_{RB}^{sb} \cdot N_{sb}}}} \right)}\mspace{20mu}{i = \left\{ {{\begin{matrix}\left\lfloor {n_{s}/2} \right\rfloor & {{inter} - {{subframe}\mspace{14mu}{hopping}}} \\n_{s} & {{{intra}\mspace{14mu}{and}\mspace{14mu}{inter}} - {{subframe}\mspace{14mu}{hopping}}}\end{matrix}\mspace{20mu}{n_{PRB}\left( n_{s} \right)}} = \left\{ {{\begin{matrix}{{\overset{\sim}{n}}_{PRB}\left( n_{s} \right)} & {N_{sb} = 1} \\{{{\overset{\sim}{n}}_{PRB}\left( n_{s} \right)} + \left\lceil {N_{RB}^{NO}/2} \right\rceil} & {N_{sb} > 1}\end{matrix}\mspace{20mu}{\overset{\sim}{n}}_{VRB}} = \left\{ \begin{matrix}n_{VRB} & {N_{sb} = 1} \\{n_{VRB} - \left\lceil {N_{RB}^{HO}/2} \right\rceil} & {N_{sb} > 1}\end{matrix} \right.} \right.} \right.}} & {{Equation}\mspace{14mu} 15}\end{matrix}$

In Equation 15, N_(sb) is the number of subbands provided by higherlayer signaling, and may be obtained from a scheduling grant. N_(RB)^(HO), which is a PUSCH hopping offset (pusch-HoppingOffset), isprovided from an higher layer.

N_(sb) is the number of subbands signaled from the upper layer, and thenumber of resource blocks of each subband N_(RB) ^(sb) may be calculatedby Equation 16.

$\begin{matrix}{N_{RB}^{sb} = \left\{ \begin{matrix}N_{RB}^{UL} & {N_{sb} = 1} \\\left\lfloor {\left( {N_{RB}^{UL} - N_{RB}^{HO} - {N_{RB}^{HO}{mod}\; 2}} \right)/N_{sb}} \right\rfloor & {N_{sb} > 1}\end{matrix} \right.} & {{Equation}\mspace{14mu} 16}\end{matrix}$

N_(RB) ^(UL) denotes the number of uplink resource blocks.

The hopping function ƒ_(hop)(i) is expressed by Equation 17 below.

$\begin{matrix}{{f_{hop}(i)} = \left\{ \begin{matrix}0 & {N_{sb} = 1} \\{\begin{pmatrix}{{f_{hop}\left( {i - 1} \right)} +} \\{\sum\limits_{k = {{i \cdot 10} + 1}}^{{i \cdot 10} + 9}{{c(k)} \times 2^{k - {({{i \cdot 10} + 1})}}}}\end{pmatrix}{mod}\; N_{sb}} & {N_{sb} = 2} \\{\begin{pmatrix}{{f_{hop}\left( {i - 1} \right)} +} \\\begin{matrix}\left( {\sum\limits_{k = {{i \cdot 10} + 1}}^{{i \cdot 10} + 9}{{c(k)} \times 2^{k - {({{i \cdot 10} + 1})}}}} \right) \\{{{mod}\;\left( {N_{sb} - 1} \right)} + 1}\end{matrix}\end{pmatrix}{mod}\; N_{sb}} & {N_{sb} > 2}\end{matrix} \right.} & {{Equation}\mspace{14mu} 17}\end{matrix}$

Further, the mirroring function ƒ_(m)(i) is expressed by Equation 18below.

$\begin{matrix}{{f_{m}(i)} = \left\{ \begin{matrix}{i\;{mod}\; 2} & \begin{matrix}{N_{sb} = {{1\mspace{14mu}{and}\mspace{14mu}{intra}\mspace{14mu}{and}\mspace{14mu}{inter}} -}} \\{{subframe}\mspace{14mu}{hopping}}\end{matrix} \\{{CURRENT\_ TX}{\_ NB}\;{mod}\; 2} & \begin{matrix}{N_{sb} = {{1\mspace{14mu}{and}\mspace{14mu}{inter}} -}} \\{{subframe}\mspace{14mu}{hopping}}\end{matrix} \\{c\left( {i \cdot 10} \right)} & {N_{sb} > 1}\end{matrix} \right.} & {{Equation}\mspace{14mu} 18}\end{matrix}$

In Equation 18, CURRENT_TX_NB denotes the number of times oftransmission of a transport block. c(i) is a pseudo-random sequence. Inthe case of frame structure type 1, c(i) is initialized asc_(init)=N_(ID) ^(cell). In case of frame structure type 2, c(i) isinitialized as c_(init)=2⁹ (n_(f) mod 4)+N_(ID) ^(cell) at the beginningof each frame. For c(i), Section 7.2 of 3GPP TS 36.211 may bereferenced.

In Type 2 PUSCH hopping, hopping and mirroring are performed on asubband basis according to the hopping function ƒ_(hop)(i). Mirroring isapplied in a way that reverses the order of the resources used in thesubband. As described in Equation 17, the hopping function may bedetermined based on the pseudo-random sequence c(k). Herein, thepseudo-random sequence c(k) is a function of cell ID and the mirroringpattern is also a function of cell ID. Therefore, all UEs in the samecell have the same hopping pattern. That is, cell-specific mirroring maybe applied to Type 2 PUSCH hopping.

FIG. 15 illustrates an example of type 2 PUSCH hopping.

In FIG. 15, type 2 PUSCH hopping when the number of subbands N_(sb) is 4is illustrated. In FIG. 15(a), hopping is performed by one subband forthe first slot and two subbands for the second slot with respect to avirtual resource block 601. In FIG. 15(b), mirroring is applied to thesecond slot.

In D2D communication, in order to obtain frequency diversity, frequencyhopping may be applied in determining a transmission resource block.However, if the above-described PUSCH frequency hopping pattern ofLTE/LTE-A is applied to D2D communication, the following issues may beraised. In the current D2D communication, only the inter-subframehopping is used. Therefore, to use the LTE type 1 PUSCH hopping patterndescribed above, determination of a hopping pattern by CURRENT_TX_NBneeds to be corrected. For example, the value of CURRENT_TX_NB may bereplaced with a subframe value. For example, the even subframes mayconform to the hopping pattern of the first slot of LTE type 1 PUSCHhopping and the odd subframes may conform to the hopping pattern of thesecond slot of LTE type 1 PUSCH hopping. Also, as described above, a D2Dresource pool may be configured, and when frequency hopping is performedwithin the configured D2D resource pool, the bandwidth and offset(N_(RB) ^(HO) or Ñ_(RB) ^(HO)) of frequency hopping need to be modified.In the following description, a D2D resource pool may refer to aresource block pool.

Embodiment 1

When there is a frequency pool configured in D2D communication, theequations of the LTE PUSCH frequency hopping described above may bechanged such that the D2D signals may be frequency-hopped within theconfigured frequency pool. For example, when an LTE type 1 PUSCH hoppingpattern or an LTE type 2 PUSCH hopping pattern is applied to D2Dcommunication, the bandwidth of frequency hopping may be configured fromthe start PRB of the D2D resource pool having a contiguous frequencyband to the end PRB of the D2D resource pool. In addition, for example,the frequency hopping offset may be set to twice the numeric value ofthe start PRB of the D2D resource pool having a contiguous frequencybandwidth.

For example, in the following description, the smallest PRB number of aD2D resource pool (e.g., a D2D resource pool with a contiguous frequencyband) may be defined as n_(PRBSTART) ^(D2D), and the largest PRB numberof the D2D resource pool may be defined as n_(PRBEND) ^(D2D).

Embodiment 1-1

For the LTE type 1 PUSCH hopping pattern, the hopping bandwidth N_(RB)^(PUSCH) may be defined as N_(RB) ^(PUSCH)=n_(PRBEND)^(D2D)−n_(PRBSTART) ^(D2D)+1.

Embodiment 1-2

For the LTE type 1 PUSCH hopping pattern, the hopping offset Ñ_(RB)^(HO) may be defined as Ñ_(RB) ^(HO)=N_(RB) ^(HO)=2×n_(PRBSTART) ^(D2D).

Embodiment 1-3

For the LTE type 2 PUSCH hopping pattern, Equation 16 described abovemay be replaced by Equation 19 below.

$\begin{matrix}{N_{RB}^{sb} = \left\{ \begin{matrix}N_{RB}^{PUSCH} & {N_{sb} = 1} \\\left\lfloor \left( {N_{RB}^{PUSCH}/N_{sb}} \right\rfloor \right. & {N_{sb} > 1}\end{matrix} \right.} & {{Equation}\mspace{14mu} 19}\end{matrix}$

In Equation 19, N_(RB) ^(PUSCH) may be defined as N_(RB)^(PUSCH)=n_(PRBEND) ^(D2D)−n_(PRBSTART) ^(D2D)+1.

Embodiment 1-4

For the LTE type 2 PUSCH hopping pattern, the hopping offset N_(RB)^(HO) may be defined as N_(RB) ^(HO)=2×n_(PRBSTART) ^(D2D).

Embodiment 1-5

For the LTE type 2 PUSCH hopping pattern,

$i = \left\{ \begin{matrix}\left\lfloor {n_{s}/2} \right\rfloor & {{inter} - {{subframe}\mspace{14mu}{hopping}}} \\n_{s} & {{{intra}\mspace{14mu}{and}\mspace{14mu}{inter}} - {{subframe}\mspace{14mu}{hopping}}}\end{matrix} \right.$in Equation 15 may be replaced with i=└n_(s)/2┘.

FIG. 16 illustrates a D2D resource pool according to an embodiment.

Multiple D2D resource pools may be co-located in the frequency domainfor a period of time. For example, as shown in FIG. 16, there may be twoD2D resource pools. The two resource pools overlap in time range C. Inthis case, in the case where resource pool A and resource pool B performfrequency hopping only in the resource pool of itself, frequency hoppingmay be performed according to Embodiment 1 to Embodiment 1-5 describedabove. However, in order to obtain higher frequency diversity, the datain the resource pool may be hopped as they are transferred to differentfrequency pools. For example, in FIG. 16, data in resource pool A may behopped between resource pools A and B every subframe.

Embodiment 2

In the following embodiments, frequency hopping between resource poolsis described. In the following description, two or more resource poolsoverlap each other within a specific time range. The number of resourcepools between which frequency hopping is performed among mutuallyoverlapping resource pools is defined as N_(R)(N_(R)≥2). N_(R) resourcepools may not consist of contiguous frequency resources. Each of theN_(R) frequency pools may be configured as an independent resource pool.Also, the N_(R) frequency pools may be a part of one resource poolconsisting of non-contiguous frequency resources in the frequencydomain, with each part having contiguous frequency resources.

Embodiment 2-1

N_(R) frequency pools between which frequency hopping is performed maybe predefined or may be announced to the UE by Radio ResourceControl(RRC) signaling. The size of the band of the frequency poolhaving the smallest frequency band among the frequency pools may bedefined as N_(min,frequency). In this case, frequency hopping may beapplied only to frequency bands corresponding to N_(min,frequency) amongN_(R) frequency pools. This limitation is intended to prevent thefrequency band of hopped data from exceeding the frequency band of afrequency pool (e.g., a frequency pool having a frequency band of sizeN_(min,frequency)) when frequency hopping is applied to a frequency bandof a larger size.

Embodiment 2-2

N_(R) frequency pools among which frequency hopping is performedmutually may be arranged from a frequency pool having the start PRBwhose index is the smallest among the frequency pools. For example, theresource pools may be indexed as resource pool 1, resource pool 2, . . ., resource pool N_(R)−1, starting with a resource pool having thesmallest start PRB index. Data to be hopped in each resource pool i(i=0, 1, 2, . . . , −1) may be hopped to the resource pool(i+N_(hopping))mod N_(R) in the next subframe. Here, N_(hopping) may beannounced to the UE through higher layer signaling or DCI, or may bepreset. The data to be hopped may be hopped according to the value ofCURRENT_TX_NB described above.

Also, for data hopped to another resource pool, mirroring may be appliedwithin the hopped resource pool. In addition, for data hopped to anotherresource pool, the modified LTE type ½ PUSCH hopping described above inconnection with Embodiments 1 to 1-5 may be applied to data hopped toanother resource pool.

Embodiment 2-3

N_(R) frequency pools among which frequency hopping is performedmutually may be sorted in ascending order of the index of each start PRBthereof. The resource pools may be indexed (or re-indexed) as resourcepool 1, resource pool 2, . . . , resource pool N_(R)−1, starting with aresource pool having the smallest start PRB index. PRBs in the D2Dresource pool may be assigned a virtual PRB index (or number) leadingfrom resource pool 0 to resource pools having contiguous numbers. Forexample, PRB indexes 0 and 1 may be used for uplink signal transmission,PRB indexes 2, 3 and 4 are used for D2D resource pool 0, PRB indexes 5,6 and 7 are used to transmit uplink signals, and PRB indexes 8, 9, and10 may be used for D2D resource pool 1. Thus, contiguous D2D resourcepool 0 and D2D resource pool 1 whose numbers are contiguous include PRBindexes 2, 3, 4, 8, 9, and 10. In this case, 0, 1, 2, 3, 4, and 5, whichare virtual PRB numbers (indexes), may be given to PRB indexes 2, 3, 4,8, 9, and 10. Therefore, a virtual PRB number starts in D2D resourcepool 0, and a contiguous virtual PRB numbers may be given between theD2D resource pools. That is, the resource blocks of the D2D resourcepools may be arranged in ascending order of resource block number in theresource pool.

For example, the virtual PRB number n_(D2DVRB) may be modified accordingto n_(D2DVRB)′→(n_(D2DVRB)+N_(hopping,RB))mod N_(Σ). Herein, N_(Σ) isthe sum of frequency bands of N_(R) resource pools among which frequencyhopping is performed mutually, N_(hopping,RB) is a unit of resourceblocks in which hopping is performed. N_(hopping,RB) may be set to themaximum value or minimum value of the frequency bandwidth of each ofN_(R) resource pools in which hopping is performed. N_(hopping,RB) maybe provided to the UE via higher layer signaling or DCI, or may be apredetermined value.

The modified virtual PRB numbers are mapped to actual PRB numbersaccording to the above description. For example, PRB indexes 0 and 1 maybe used for uplink signal transmission, PRB indexes 2, 3 and 4 may beused for D2D resource pool 0, and PRB indexes 5, 6, and 7 may be usedfor uplink signal transmission, and PRB indexes 8, 9, and 10 may be usedfor D2D resource pool 1. In this case, 0, 1, 2, 3, 4, and 5, which arevirtual PRB numbers (indexes), may be given to PRB indexes 2, 3, 4, 8,9, and 10. Thereafter, the virtual PRB numbers may be modified ton_(D2DVRB)′, virtual PRB numbers 0, 1, 2, 3, 4, and 5 modified asdescribed above. The modified virtual PRB numbers n_(D2DVRB)′, 0, 1, 2,3, 4, and 5, may be mapped to actual PRB numbers 2, 3, 4, 8, 9, and 10.

Embodiment 2-4

Regarding Embodiments 2-1 to 2-3 described above, for example, a casewhere there are two D2D resource pools or a case where one D2D resourcepool is composed of two resource regions having contiguous frequencieswill be described. When frequency hopping is performed only in tworesource pools (or two resource regions), the above-described LTE type ½PUSCH hopping pattern is modified as in Embodiments 2-4-1 to 2-4-5described below and applied. In the following description, the smallervalue of the start PRB indexes of the two D2D resource pools (or tworesource regions) is defined as n_(PRBSTART) ^(D2D,0), and the greatervalue is defined as n_(PRBSTART) ^(D2D,1).

Embodiment 2-4-1

For the LTE type 1 PUSCH hopping pattern, the hopping bandwidth N_(RB)^(PUSCH) may be defined as N_(RB) ^(PUSCH)=2×(n_(PRBSTART)^(D2D,1)−n_(PRBSTART) ^(D2D,0)).

Embodiment 2-4-2

For the LTE type 1 PUSCH hopping pattern, the hopping offset Ñ_(RB)^(HO) may be defined as Ñ_(RB) ^(HO)=N_(RB) ^(HO)2×n_(PRBSTART)^(D2D,0).

Embodiment 2-4-3

For the LTE type 1 PUSCH hopping pattern, ñ_(PRB)(i) may be defined asñ _(PRB)(i)=(└N _(RB) ^(PUSCH)/2┘+ñ _(PRB) ^(S1)(i))mod N _(RB) ^(PUSCH)orñ _(PRB)(i)=(−└N _(RB) ^(PUSCH)/2┘+ñ _(PRB) ^(S1)(i))mod N _(RB)^(PUSCH).

Embodiment 2-4-4

For the LTE type 2 PUSCH hopping pattern, Equation 16 may be replaced byEquation 20 below.

$\begin{matrix}{N_{RB}^{sb} = \left\{ \begin{matrix}N_{RB}^{PUSCH} & {N_{sb} = 1} \\\left\lfloor \left( {N_{RB}^{PUSCH}/N_{sb}} \right\rfloor \right. & {N_{sb} > 1}\end{matrix} \right.} & {{Equation}\mspace{14mu} 20}\end{matrix}$

In Equation 20, N_(RB) ^(PUSCH)=2×(n_(PRBSTART) ^(D2D,1)−n_(PRBSTART)^(D2D,0)).

Embodiment 2-4-5

For the LTE type 2 PUSCH hopping pattern, the hopping offset N_(RB)^(HO) may be defined as N_(RB) ^(HO)=2×n_(PRBSTART) ^(D2D,0).

Embodiment 2-5

A virtual resource space configured only by D2D resource pools maycreated, and the modified LTE type ½ PUSCH hopping may be performedwithin the virtual resource space. Then, the virtual resource space maybe mapped back to the physical resource space. For example, the indexesof start PRBs of N_(R) resource pools in which frequency hopping isperformed mutually may be arranged in ascending order from the smallestone. The resource pools may be indexed as resource pool 1, resource pool2, . . . , resource pool N_(R)−1 from the resource pool whose start PRBhas the smallest index. PRBs in the D2D resource pool may be assigned avirtual PRB index (or number) leading from resource pool 0 to resourcepools having contiguous numbers. For example, PRB indexes 0 and 1 may beused for uplink signal transmission, PRB indexes 2, 3 and 4 are used forD2D resource pool 0, PRB indexes 5, 6 and 7 are used to transmit uplinksignals, and PRB indexes 8, 9, and 10 may be used for D2D resourcepool 1. Thus, D2D resource pool 0 and D2D resource pool 1 whose numbersare contiguous include PRB indexes 2, 3, 4, 8, 9, and 10. In this case,0, 1, 2, 3, 4, and 5, which are virtual PRB numbers (indexes), may begiven to PRB indexes 2, 3, 4, 8, 9, and 10. Therefore, a virtual PRBnumber starts in D2D resource pool 0, and a contiguous virtual PRBnumbers may be given between the D2D resource pools.

In this case, LTE type 1 PUSCH hopping may be used by modifying theequation of the LTE type 1 PUSCH hopping as Ñ_(RB) ^(HO)=N_(RB) ^(HO)=0and N_(RB) ^(PUSCH)=N_(Σ). N_(Σ) is the sum of the frequency bands ofN_(R) resource pools in which frequency hopping is performed mutually.

LTE type 2 PUSCH hopping may also be used by replacing Equation 16 ofthe above-described LTE Type 2 PUSCH hopping with Equation 21 below andmodifying the Equation 21 with N_(RB) ^(PUSCH)=N_(Σ) and N_(RB) ^(HO)=0.

$\begin{matrix}{N_{RB}^{sb} = \left\{ \begin{matrix}N_{RB}^{PUSCH} & {N_{sb} = 1} \\\left\lfloor \left( {N_{RB}^{PUSCH}/N_{sb}} \right\rfloor \right. & {N_{sb} > 1}\end{matrix} \right.} & {{Equation}\mspace{14mu} 21}\end{matrix}$

The modified virtual PRB numbers may be mapped to the actual PRB numbersagain as described above. For example, PRB indexes 0 and 1 may be usedfor uplink signal transmission, PRB indexes 2, 3 and 4 are used for D2Dresource pool 0, PRB indexes 5, 6 and 7 are used to transmit uplinksignals, and PRB indexes 8, 9, and 10 may be used for D2D resourcepool 1. In this case, the virtual PRB numbers 0, 1, 2, 3, 4 and 5assigned to the actual PRB indexes 2, 3, 4, 8, 9 and 10 may be hoppedaccording to the modified LTE type ½ PUSCH hopping and converted intomodified virtual PRB numbers. The modified virtual PRB numbers 0, 1, 2,3, 4, and 5 may be mapped to actual PRB numbers 2, 3, 4, 8, 9, and 10,respectively.

Embodiment 3

When the frequency hopping rule is followed in D2D communication, thehopped transmission data may be outside of the resource pool. In thiscase, the transmission data out of the resource pool due to frequencyhopping may be dropped. That is, the transmission data may betransmitted only on the corresponding frequency resource.

Further, if the data hopped according to the frequency hopping rule inD2D communication cannot be transmitted on contiguous frequencyresources, the data may be dropped. That is, the data may be configuredto be transmitted on contiguous frequency resources. In other words,transmission of data from the UE in D2D communication may occur only oncontiguous frequency resources (i.e., contiguous PRBs).

For example, PRB indexes 0 and 1 may be used for uplink signaltransmission, PRB indexes 2, 3 and 4 are used for D2D resource pool 0,PRB indexes 5, 6 and 7 are used to transmit uplink signals, and PRBindexes 8, 9, and 10 may be used for D2D resource pool 1. In this case,the data of PRB indexes 2, 3, and 4 may be transmitted only within theD2D resource pool 0. That is, if the data of the hopped PRB indexes 2,3, and 4 are mapped to the actual PRB indexes 5, 6, and 7, transmissionof the corresponding data may be dropped.

The embodiments described above are constructed by combining elementsand features of the present invention in a predetermined form. Theelements or features should be considered selective unless explicitlymentioned otherwise. Each of the elements or features can be implementedwithout being combined with other elements. In addition, some elementsand/or features may be combined to configure an embodiment of thepresent invention. The ordering of the operations discussed in theembodiments of the present invention may be changed. Some elements orfeatures of one embodiment may also be included in another embodiment,or may be replaced by corresponding elements or features of anotherembodiment. It is apparent that claims that are not explicitly cited ineach other in the appended claims may be presented in combination as anembodiment of the present invention or included as a new claim bysubsequent amendment after the application is filed.

The present invention may be carried out in specific forms other thanthose set forth herein without departing from the spirit and essentialcharacteristics of the present invention. Therefore, the aboveembodiments should be construed in all aspects as illustrative and notrestrictive. The scope of the invention should be determined by theappended claims and their legal equivalents, and all changes comingwithin the meaning and equivalency range of the appended claims areintended to be embraced therein.

INDUSTRIAL APPLICABILITY

Although a frequency hopping method and device for D2D(Device-to-Device) communication have been described with reference toexamples applied to the 3GPP LTE system, they are applicable to variouswireless communication systems other than the 3GPP LTE system.

The invention claimed is:
 1. A method of transmitting a Device-to-Device (D2D) signal by a user equipment (UE) in D2D communication, the method comprising: receiving information related to a resource block pool including two resource regions for transmitting the D2D signal, wherein each of the two resource regions includes resource blocks (RBs); performing frequency hopping to the RBs based on a predefined hopping pattern; and transmitting the D2D signal based on a result of the frequency hopping for the RBs, wherein the information related to the resource block pool is received via higher layer signaling, wherein the D2D signal is transmitted only when the RBs are mapped to consecutive physical resource blocks (PRBs) in a subframe by the frequency hopping, and wherein each of the consecutive PRBs includes contiguous subcarriers.
 2. The method according to claim 1, wherein the higher layer signaling is Radio Resource Control (RRC) signaling.
 3. The method according to claim 1, wherein the D2D signal is dropped when the RBs are not mapped to consecutive PRBs in the subframe by frequency hopping.
 4. The method according to claim 1, wherein the frequency hopping comprise inter-subframe hopping.
 5. The method according to claim 1, wherein the predefined hopping pattern is configured based on Long Term Evolution (LTE) type 1 Physical Uplink Shared Channel (PUSCH) hopping or LTE type 2 PUSCH hopping.
 6. The method according to claim 1, wherein resource blocks of one of the two resource regions are not contiguous with resource blocks of the other resource region.
 7. A user equipment (UE) for transmitting a D2D signal in Device-to-Device (D2D) communication, the UE comprising: a memory; and a processor connected to the memory, wherein the processor is configured to: receive information related to a resource block pool including two resource regions for transmitting the D2D signal, wherein each of the two resource regions includes resource blocks (RBs), perform frequency hopping to the RBs based on a predefined hopping pattern, and transmit the D2D signal based on a result of the frequency hopping for the RBs, wherein the information related to the resource block pool is received via higher layer signaling, wherein the D2D signal is transmitted only when the RBs are mapped to consecutive physical resource blocks (PRBs) in a subframe by frequency hopping, wherein each of the consecutive PRBs includes contiguous subcarriers.
 8. The UE according to claim 7, wherein the higher layer signaling is Radio Resource Control (RRC) signaling.
 9. The UE according to claim 7, wherein the D2D signal is dropped when the RBs are not mapped to consecutive PRBs in the subframe by frequency hopping.
 10. The UE according to claim 7, wherein the frequency hopping comprises inter-subframe hopping.
 11. The UE according to claim 7, wherein the predefined hopping pattern is configured based on Long Term Evolution (LTE) type 1 Physical Uplink Shared Channel (PUSCH) hopping or LTE type 2 PUSCH hopping.
 12. The UE according to claim 7, wherein resource blocks of one of the two resource regions are not contiguous with resource blocks of the other resource region. 